In his article on medieval Greek commentaries made up entirely of chains of quotations from the Fathers — catenas, as they are called today — Devreesse has some good material on each of the four gospels on Eusebius. This is very relevant to the translation of the remains of Eusebius’ Gospel Questions and Solutions. Here is the entry on Matthew’s gospel, run into English. I have split the main paragraph so each item is separate.
Eusebius — Of the work περὶ διαφωνίας εὐγγελίων [on the differences in the gospels] composed by Eusebius, different catenas give us different extracts. It was divided into two parts (Patrologia Graeca vol. 22, col. 879-1006). The first part, relating to the genealogies [of Jesus] comprised two books; it was dedicated to Stephanus. The second, one book only, concerning the disagreement of the evangelists on some texts of the Passion, was addressed to Marinus.
In Poussines [=Possinus], Cramer, and in manuscript Vatican gr. 1618 (on Matthew, 1:1-21) there are various citations which derive from questions 1, 2 and 3 of To Stephanus. Those which Poussines gives have been reproduced, PG, 22, cols. 972-976, with two others.
One fragment on the name of Jesus (1, 3-8b) placed sometimes in the mouth of Origen belongs in reality to Eusebius (cf. G. Mercati, Un supposto frammento di Origene, in Revue biblique 17, 1910, p. 76-79).
Sometimes the scholiast seems to have hesitated about the attribution to Eusebius (cf. Cramer, p. 12, 15).
As for the questions To Marinus, some fragments can be found in Cramer p. 251-256 which belong to this.
Some other citations can be met with in Cramer, p. 56 (Mt. 7:27), and 81 (Mt 10:34); Pousinnes, p. 35 (Mt 3:3), and 145 (Mt 10:24-25). Perhaps all this Eusebian material is analogous to some that was signalled in the Bodleian Library manuscript Laud 33, fol. 80b (Harnack-Preuschen, Geschichte, vol. 1, p.577).
Zahn has published (Geschichte d. Neutestamentl. Kan. vol. 2, p. 915) another scholion of Eusebius on Matthew 16:9-20, from manuscript Moscow Holy Synod 139.
I need to get hold of the Mercati and Zahn articles. It all reinforces the impression of fragments all over the place. Any editor of this material will have a considerable job simply to assemble the raw materials!